1. Field of the Invention
The present invention relates generally to electrical connectors. More specifically, the present invention concerns connectors for establishing electrical continuity between conductors in a first tubular element and corresponding conductors in a mating second tubular element, where said connectors are suited for use in a high pressure, conductive fluid environment.
2. Description of the Technical Problem
The search for and production of valuable subsurface fluids, such as hydrocarbons, carbon dioxide, helium and geothermally heated water, typically requires that a borehole be drilled from the surface of the earth to the strata bearing the subsurface fluid. The drilling of such boreholes is accomplished by a drill bit supported and controlled by a drilling rig located at the earth's surface. A tubular column known as the drill string connects the drill bit to the drilling rig. In rotary drilling, utilized in the majority of modern drilling operations, the drill string serves to transmit both torque and drilling fluid from the drilling rig to the drill bit. The drill string is composed of tubular elements which are detachably joined to one another at threaded connections termed tool joints.
In certain applications it is desirable to provide the drill string or bit with electrical instrumentation. Suitable instrumentation can be utilized to record the condition of the drill bit, log formation properties in the course of drilling operations, measure various borehole conditions and control electro-mechanical apparatus in the drill string or bit. In certain schemes of operation, monitoring the output of downhole instrumentation or controlling downhole apparatus from the surface requires that one or more electrical conductors extend along the drill string and across at least one of the tool joints.
The nature of tool joints presents formidible obstacles to the reliable transmission of electrical signals along a drill string incorporating an electrical conductor. Tool joints are composed of two portions, a pin and a box. The pin has exposed tapered threads which correspond to recessed tapered threads of the box. A pin is connected to one end of each element of the drill string and a box to the other end such that the various elements of the drill string can be threaded one to the other. As the borehole deepens, additional joints are threaded onto the end of the drill string to increase its length. The tool joints must be adapted to accept both axial loading, often from the weight of as much as an 8,000 meter length of drill pipe, and the significant torsional loadings imposed in the course of rotary drilling. Additionally, the tool joints are exposed to much rough usage, abrasion and shock loadings in the course of making up and breaking out the threaded connections in drilling operations.
Transmitting an electrical signal across a tool joint can be accomplished by providing mating electrical contacts at interfacing portions of the adjoining elements of the drill string. However, this use of a contact type electrical connector attached to the tool joint poses many difficulties. The use of conductive drilling fluids at high downhole pressures creates a significant insulation problems. The need for a fluid passageway with low flow resistance through the conduit presents significant size and configuration limitations on the connector. The rough handling, extreme vibrations and abrasive particulate matter to which the drill string is subjected in the course of drilling establish significant reliability obstacles. Further, rig efficiency concerns and the potential for human error render it highly desirable that the electrical connection require a minimum of special action on the part of the drilling crew in making up the tool joint.
The present invention is directed to advantageously meeting the requirements listed above.